1. Field of the Invention
The present invention relates to an image processing apparatus and an image communication apparatus, and more specifically to an image processing apparatus and an image communication apparatus having a plurality of compression methods in which image information is compressed by a designated compression method.
2. Related Background Art
The compression methods of image information include, in addition to an MMR method for use with G4 facsimile apparatus, a method defined by JPEG (hereinafter referred to as JPEG method), and this JPEG method has widely spread in recent years. The JPEG method involves converting color image information into information of frequency region, and quantizing and encoding the coefficients obtained by conversion. Both the JPEG method and the MMR method allow for the designation of resolution.
Since the total number of pixels generally decreases with lower resolution, the total number of compressed data also decreases, while at the same time image quality is degraded with lower density of pixels. Conversely, with higher resolution, the quantity of image data after compressed increases, with the image quality improved.
However, the JPEG method involves a quantization table, in addition to the resolution, as the factor for determining the image quality. The employment of quantization table stressing high frequency components allows for the reproduction of fine variations in image with enhanced ability of reproducing high frequency components, resulting in improved image quality. Of course, the number of coefficients of high frequency components increases, and proportionally, the total quantity of image data after compressed also increases. The use of quantization table with high frequency components stressed has the same effects as if data is compressed at high resolutions.
With the spread of JPEG method, a color facsimile apparatus has been devised in which transmission for color image information with the JPEG method is enabled by providing an encode/decode circuit of the JPEG method on the G4 facsimile apparatus. In one configuration, the apparatus allows for the selection of resolution with the MMR method by the use of a resolution selection key, but has a fixed quantization table with the JPEG method.
It should be noted that the resolution selection key is configured to be adapted to the MMR method, i.e., a transmission format of image data in G4 facsimile, but only allow for the selection from a plurality of fixed resolutions, such as 200 dpi.times.200 dpi, 300 dpi.times.300 dpi, and 400 dpi.times.400 dpi.
In the conventional configurations, no image quality adjusting ability by the selection of quantization table with the JPEG method has been utilized.